The present invention relates to lubricant testers and, in particular, to a portable friction tester having balanced, opposed test bushings that are biased with springs, levers and/or pressure to load a rotating rotor (e.g. race, disc or sphere) and wherefrom numerous variables (e.g. torque, angular speed, audio and temperature outputs) are monitored to test the relative lubricating properties of lubricants (e.g. commercial oils and greases).
Classical friction is the resistance to relative motion between two surfaces as a consequence of slip-sticking, plastic deformation and/or welding that occurs with the ultimate generation of heat. Friction can be measured quantitatively and/or qualitatively by visual examination of tested samples. In physics, friction is an energy process that converts the ordered motion of some object into disordered motion and heat.
An important engineering concept in the study of friction and lubrication is the xe2x80x9clubrication parameterxe2x80x9d (LP). The lubrication parameter considers friction and lubricity in relation to three factors: sliding speed, load and viscosity of a lubricant sample. The relative control of these three factors determines not only the degree of friction for a specific sample but also wear. Depending upon the physical parameters that indicate friction for a particular test, quantitative measures can be obtained in various units, depending upon the physical property that is monitored and measured.
Wear between two mating surfaces experiencing friction can also elicit a qualitative measure of friction. The degree of wear is found by visual examination of the two mating surfaces after a test. Wear can also be determined, for example, by methods such as particle count analysis and/or magnetic or chemical examination of debris left in a lubricant sample after a test. However, the detection of wear from friction is not a primary goal of this invention because friction analysis and wear analysis are highly dissimilar and not comparable disciplines. For example precise wear analysis would take much longer times of operation and greater PSI loading than this invention is designed for.
Tribology is the study of lubrication and lubricants and their related coefficients of friction, viscosity and lubricity, among other relevant physical properties and parameters. A variety of testers have been developed to test the lubrication properties of all types of lubricants and materials in their various states (i.e. liquid, solid and gas) from grease to oil to plastics, to name a few lubricants. The knowledge of these properties and pertinent wear characteristics allows for the design of improved machines.
Some examples of devices used to test rubber are shown at U.S. Pat. Nos. 6,167,745; 6,334,358 and 6,349,587. Some lubrication/friction testing assemblies are shown at U.S. Pat. Nos. 5,388,442; 5,932,790; 6,145,370 and 6,167,745. Some oil testing assemblies are shown at U.S. Pat. Nos. 3,990,960 and 6,365,413. A force and position related test system for tribological materials is shown at U.S. Pat. No. 5,679,883 and a strain measuring tribological test assembly is shown at U.S. Pat. No. 6,363,798.
The present improved tester was developed to provide a portable, yet accurate lubricant tester that employs an electric or hydraulic motor to drive a rotating surface or rotor (e.g. a disc, race or sphere) at a stable and measured but not necessarily constant speed. At least one pair of sample holders (e.g. bushings) are maintained with a controlled bias to present a constant, known load with the rotating surface in the presence of a lubricant sample (e.g. oil, grease or solid film). The specific loading is measured in pounds force or pressure in pounds per square inch (PSI) and can be adjusted with different combinations of bushings and/or bias springs and/or weighted levers and/or pneumatic/hydraulic pressure to direct the bushings into contact with the rotating surface.
The motor runs briefly for several seconds as two lubricated metal surfaces (e.g. steel or aluminum or copper or iron) are pressed against each other. A loss of RPM, heat, noise and the consumption of power at the motor reflect the resultant drag. The latter outputs can be measured in terms of shaft torque, temperature degrees, RPM, decibels and frequency of noise, hydraulic PSI, amperage draw or voltage drain, among other values. The observed/measured values do not directly yield a calculated coefficient of friction for each oil sample. The values however reflect numbers that can be compared to other samples to provide a relative comparison and give a history. The measured results can also be captured on video or film and/or be analyzed by computer.
It is a primary object of the invention to provide a portable lubricant tester that supports at least two sample lubricant holders into balanced, opposing contact with a moving surface.
It is further object of the invention to provide a lubricant tester wherein bushings soaked in a sample lubricant and containing a wick soaked in the lubricant or lined with a solid film sample are biased under a known force in opposed resistance to a rotor (e.g. rotating disc, race or spheroid).
It is further object of the invention to provide a generic motor, either electric or hydraulic, typically about one horsepower to drive the rotor to overcome the opposed loading applied by paired sets of sample support bushings.
It is a further object of the invention to provide sample holders or xe2x80x9ccylinder blocksxe2x80x9d having multiple bores that are symmetrically arranged toward a rotating disc, race or ball rotor and that each contain sample support bushings and resilient biasing members for directing the bushings into contact with the disc, race or ball rotor.
It is further object of the invention to provide a cylinder block having bores that define upper and lower cylinders relative to an intermediate cavity within which a disc rotates and wherein the upper and lower cylinders contain sample supporting bushings and springs to bias the bushings into orthogonal contact with the rotating disc.
It is further object of the invention to resiliently bias each bushing with one or more springs having calibrated spring constants.
It is further object of the invention to resiliently bias each bushing with weighted lever arms.
It is further object of the invention to resiliently bias each bushing with a controlled pneumatic or hydraulic pressure.
It is further object of the invention to provide one or more cylinder blocks having radially directed bores that contain sample supporting bushings biased with springs, weighted levers or fluid pressure to direct the bushings into tangential contact and load a rotating rotor.
The foregoing objects, advantages and distinctions of the invention are obtained in three presently preferred test assemblies. In one preferred construction, the assembly provides an electric motor secured to a rigid base plate. A metal disc is mounted to rotate from the motor drive shaft. Mounted to the base plate are one or more symmetrically positioned cylinder blocks. Each cylinder block provides a horizontal raceway cavity that partially encompasses the disc and at least one orthogonal bore that defines first and second cylinders. The cylinders each contain appropriate test or sample support bushings lubricated with a test lubricant and one or more calibrated springs or other means that bias the bushings into contact with opposite surfaces of the disc at a known, constant force.
In another construction, a metal race or cylindrical or spherical rotor of substantial thickness is mounted to rotate on the motor drive shaft. Mounted to the base plate are one or more symmetrically positioned cylinder blocks. Each cylinder block provides a number of radially directed bores that define sample support cylinders and which cylinders are aligned in radially opposed relation to each other relative to the drive shaft and rotor. Each cylinder contains a sample support bushing and one or more calibrated springs, weighted levers or other pressurized means bias the bushing into contact with the rotor at a known, constant force.
In another construction, a metal race or spheroid rotor is mounted to rotate on the motor drive shaft. Concentrically mounted to the rotor at a supporting base plate is an annular cylinder block. The cylinder block provides several paired sets of bores that define sample support cylinders and which cylinders are aligned in radially opposed relation to each other relative to the drive shaft and rotor. Each cylinder contains a sample support bushing. Each bushing is biased to contact the rotor via a lever that pivots on an axle secured to the cylinder block. Each lever supports a calibrated weight and whereby a force multiplication (e.g. 2xc3x97 to 12xc3x97) is achieved and a known, constant load force is obtained at the rotor. The levers and weights provide identical, balanced, opposing loading forces, which generate relatively extreme frictional pressures between the bushings. The loading can be augmented or alternatively achieved with a controlled pneumatic or hydraulic pressure. As in all the embodiments, the opposed mountings of the bushings cancels extraneous conditions that may exist, other that the load forces